1. Technical Field
Compositions consistent with the present invention relate to phosphors and, more particularly, to phosphors that are efficiently excited by ultraviolet light or short-wavelength visible light to emit light.
2. Description of the Related Art
Various light emitting devices have been known that can provide light of desired colors by combining a light emitting element and a phosphor which is excited by light generated by the light emitting element and then emits light of a wavelength band different from that of the light emitting element.
Particularly, a related art light emitting device that provides white light by combining a semiconductor light emitting element, which emits ultraviolet light or short-wavelength visible light, such as a light emitting diode (LED) and a laser diode (LD), with a phosphor that uses them as an excitation light source has been proposed as a white light emitting device that is durable and consumes little power.
Various such related art white light emitting devices have been proposed, such as (1) a device combining an LED that emits blue light and a phosphor that is excited by the blue light and then emits yellow light, and (2) a device combining a plurality of LEDS that emit violet light or ultraviolet light and phosphors that emit light with colors of red, green, blue, yellow, and the like. (see e.g., Japanese Patent No. 3503139; Japanese Unexamined Patent Application Publication No. 2005-126577; and Japanese Unexamined Patent Application Publication No. 2003-110150)
However, the related art white light emitting devices described above have a few disadvantages. For example, in the related art white light emitting device (1), there is little light of a wavelength band between the blue color and the yellow color, and a color rendering property is small because there is little light of a red region obtained from the phosphor. The white light is obtained by mixing the light of the LED and the light of the phosphor. Accordingly, for example, when the application amount of the phosphor is not uniform in a production process of the related art white light emitting device, balance in the amount of light emitted by the LED and the phosphor is broken. Therefore, non-uniformity occurs also in the spectrum of the obtained white light.
The related art white light emitting device (2) is good in a color rendering property, but a phosphor having a strong excitation band in an ultraviolet light region or a short-wavelength visible light region has not been found, and thus it has been difficult to realize a high-power white light emitting device.